In a supersonic aircraft powered by turbojets, remote fans are added ahead of the turbojets and connected to them by driveshafts which take some power from the compressor rotors. This doubles the airflow and decreases the jet exhaust velocity. A remote front fan is known in the art in U.S. Pat. No. 3,161,019. His FIG. 10 shows an auxiliary compressor 62 driven by a shaft 64 controlled by a crutch and connected to a gas turbine engine 15.
The engine nacelle is like the ones in Concorde Mach 2 airliner, a long flat box slung under a wing and containing two turbojets in the rear half. The front half of the nacelle houses the intake air ducts, again like Concorde. However, our nacelle's two intake air ducts are back-to-back, like those in the USAF B-1 bomber. The air ducts curve apart from each other in the middle, therefore that space is where the remote fans are housed.
In the B-1, the air intakes start with wedge-shaped external-shock inlets (JANE's All The World's Aircraft, 1977-78, page 389.) The wedges flare left and right from a vertical knife-edge to achieve external compression by oblique shocks to the sides. We do the same. The wedges can be seen in FIGS. 2 and 3 of Paper 730348, Society of Automotive Engineers (“SAE”), also in SAE Transactions, Vol. 82, 1973, page 1139. With the airflow directed to the sides of the nacelle, a central volume of unused space is created. A similar layout is seen in Option 2 on page 43 of Mechanical Engineering, November 1962. The central volume of unused space is the lozenge-shaped grey area between two air ducts in white. In our invention, the lozenge space is where the two remote fans are located, one for each turbojet engine. The lozenge space is long, so the fans are installed in tandem. No example of this was found in the art.
The tandem fans are shaft-driven from a central gear turned by pinions connected to driveshafts extending from the turbojets. Gear drive of remote fans is in FIG. 8 of U.S. Pat. No. 3,161,019. Our fan output ejects from the nacelle bottom to produce forward thrust. Doors similar to door 35 in U.S. Pat. No. 3,900,177 will open downward from the nacelle floor, except they would be turned 180 degrees to point backward.
Driving the new fans takes some additional power from the low pressure (“LP”) turbines of the turbojet engines. It is known to open the exhaust nozzles more than the correct setting for generating maximum jet thrust. This causes a drop in the pressure within the jet pipes. The working gas flowing through the turbines undergoes greater expansion and produces more shaft work. An early example for turning a large remote rotor is U.S. Pat. No. 2,940,691. A similar instance is U.S. Pat. No. 3,678,690. A closer example is nozzle opening variation behind the LP turbine which turns a fan in U.S. Pat. No. 3,186,165.
Our two-stage remote fans take more energy to turn than single-stage units. The pressure in the jet pipe would fall too low for good turbine efficiency. More power is needed. We supercharge the turbojets during takeoff. 15% extra flow in the LP compressor of the turbojet in Concorde has been explored (SAE Paper 800732, also in SAE Transactions, Vol. 89, 1980, pages 2276, 2278, and 2280.) Its pressure ratio had to increase so that the high pressure (“HP”) compressor didn't have to be enlarged (page 2276; Note 2 on page 2281.) But in our case, the higher pressure ratio is not wanted at cruise.
A solution is to bypass the extra flow and route it to the jet pipe. This is known in the art, U.S. Pat. No. 3,070,131. His valve 34 controls the action. An alternative embodiment is to discharge the bypass flow through a secondary nozzle immediately at the side of the engine during cruise flight: Similar to the vectored thrust nozzles in the Pegasus VTOL engine (JANE's All The World's Aircraft 1987-88, page 935,) except that one flows all the time. We control the flow with a valve. FIGS. 3 and 6 of U.S. Pat. No. 3,280,560 are related.